Digital and analog information signals are frequently distorted by an offset voltage, which effectively moves the signal baseline. When the offset voltage is positive, the positive and negative peaks of the information signal increase in the positive direction; when the offset voltage is negative, the positive and negative peaks of the information signal move in the negative direction. The magnitude of the offset voltage that will cause incorrect interpretation of the information signal depends on the positive and negative amplitudes of the information signal.
An offset voltage has two components, a static component caused by inherent manufacturing tolerances of electronic components, and a dynamic component caused by temperature variations and other distortion-producing effects over time. For proper recovery of the information signal, both of these components must be removed from or nulled out of the information signal. Previous attempts to remove the offset voltage related only to the static component. According to the prior art, the static component is removed manually by the setting of a potentiometer, but no provisions are made for component aging, temperature, or other time-based effects. Thus, the information signal may still be distorted by the dynamic component of the offset voltage.
U.S. Pat. No. 3,473,131, entitled "Level-Shift Correction Circuits", discloses a signal conditioning circuit for maintaining sequential pulses of alternate polarity at the same uniform level relative to a reference level, despite undesired level shifts in some of the received pulses. A pair of signal processing channels store energy representative of the level of an incoming pulse of one polarity in one channel during the interval occupied by that pulse, after which the magnitude of the stored energy is used as a datum against which the energy stored in the other channel during the next interval of an opposite polarity pulse is compared. The channels continually alternate in their roles, and during each pulse interval the difference between the energy stored in each channel is used to derive an error signal proportional to the difference. The error signal is fed back to an input terminal for combining with the input signal and reducing the level shift thereof.